I'll start with a disclaimer:
I've tried quite literally every solution I've come across on the internet for custom content issues, and nothing's worked. I haven't seen much talk about the issue I'm having specifically so hopefully, someone here can help.

I've had the same issues with the patterns in Create-a-Style. A colossal number of patterns I have downloaded, all appear as the same pattern (cactus) both in the pattern list and when selected to recolour an object/clothing item. This has been going on for about 2+ years at this point and recently, even more CC patterns have been added to the list of casualties.

I've tried removing all mods and packages, as well as running my game from the launcher with the CC-free option. And even when there was no CC in-game, when I checked the pattern list again, all the CC patterns were still there, just instead of the cactus pattern from before, they all appear as the same mid-tone wood pattern.

I've run packages and sims3packs through different programs previously to try to find corrupt CC and did that again recently to see if anything's changed. I've also gone through and rearranged all my CC, deleted a bunch, recompressed/merged CC, etc. I've tried uninstalling patterns and reinstalling them, even re-downloading them from the original source and using the "new" file, but nothing. I'm wondering if potentially when I ran my files through CC Magic or something the first time, is when the issue started? (Like maybe I did something because if I'm honest, I'm not entirely sure how to navigate the application.) But I really can't be sure.

I'm just frustrated at this point with what to do? I can't find any actual solutions for my issue online. In any existing threads, the only responses are "make sure you install patterns like X and Y instead," which doesn't help me much. I know how to install patterns properly, but something is clearly up.

If anyone knows what to do here, I'd be forever in your debt.

After removing all custom patterns did you delete the cache files and then restart the game?

It's been awhile but I remember having a similar issue that I think was related to converting sims3pack patterns into .package which in some cases would cause a repeating pattern. Some creators would say their patterns were okay to be converted but they don't work that way or the patterns are already converted to .package but again they don't work as intended. Then there are some creators that tells you not to convert to .package because they already tested it and knows it doesn't work. Make sure the patterns you are installing is in the correct format if specified. Otherwise, trial and error to figure out which pattern(s) do not work as .package files.

Never had that specific thing happen but sounds very much like an issue that patterns made with CAP would cause. Those are the ones that don't work when extracted to package and cause the "materializing materials" error, but you still absolutely can convert them into working packages. Just takes a few more steps. And also you don't need to do the trial and error method, they are easily identified by the instance numbers - after extracting, open the package with S3PE and check for IMG resources with an instance value of 7EDD20633162E6CE. If there is one, that's your problem file. The whole issue is caused by CAP giving every pattern that same instance number. You can give it a new one as described in this quick and easy tutorial.

It could be some weird side effect of installing such patterns through CC magic, even if they're in sims3pack form. I believe it handles them differently than the launcher, tho I never use s3packs myself so can't be sure.